Roll for cold-rolling metallic sheet materials



Sept. 19, 1967 TADASHI NEMOTO E AL 3,342,058

ROLL FOR COLD-ROLLING METALLIC SHEET MATERIALJS Original Filed March 25,1963 2 Sheets-Sheet 1 Quenching femperan/re ("6) Fl 3 g L T InvErrToRsTsaag'fi nemo o ashio Vaeg aQfi Sept. 19,1967' DASH-MEMO, m 3,342,058

ROLL FOR COLD-ROLLING METALTJI'C SHEET MATERIALS Original Filed March25, 1963 2 Sheets-Sheet z Hg 20 Hg 20 Non-etching Efch/ry M712 /0%n/fr/c ac/a' M'lcmsrrucm or" me invent/Va alloy 360) (0//'quenche0 0r950'6 BY QuL 0 417,

Tadashi Nemoto, Takahagi-shi,

United States Patent 3,342,058 ROLL FOR COLD-ROLLING METALLIC SHEETMATERIALS and Toshio Yaegashi, Hitachi-shi, Japan, assignors to Hitachi,Ltd., Tokyo, Japan, a corporation of Japan Continuation of applicationSer. No. 267,757, Mar.

25, 1963. This application Oct. 28, 1966, Ser. No.

590,437 Claims priority, application Japan, Mar. 26, 1962,

37/ 11,036 2 Claims. (Cl. 72-365) This application is a continuation ofapplication Ser. No. 267,757 filed Mar. 25, 1963, now abandoned.

The present invention relates to roll materials and more particularly tothose for use in the making of hardened forging-steel rolls and has forits object to provide a roll material of the type which is highlyimproved in hardenability and wear resistance.

Cutomarily, rolls of the Sendzimir mill for cold rolling have been madeof 'a high-carbon high-chromium steel, which has heretofore beenrecommended, since the material when quenched from higher temperaturesforms a martensite including chromium carbide of high hardness and thushas a substantial wear resistance. Most recently, however, the demandfor improvements in dimension-a1 accuracy and surface luster of rolledsteel sheets has been increasing. Conventional roll materials such ashighcarbon high-chromium alloy steels have been unable to meet thisdemand due to the lack of any satisfactory wear resistance.

In View of the above difiiculty, the present invention is designed tofurnish a roll material having an extraordinarily high wear resistanceand a high hardenability.

According to the present invention, there is provided a roll materialcomprising from 1.0% to 2.5% by weight of carbon, 3% to by weight ofchromium, 0.5 to 8% by weight of molybdenum, 0.5% to 6% by weight oftungsten, 1.0% to 7.0% by weight of vanadium, not more than 0.5% byweight of silicon, and not more than 0.5 by weight of manganese, thebalance being substantially iron.

Composition limits for each of the alloying elements will now bedetailed.

Carbon forms carbides in the alloy, which are critically important forobtaining a desired wear resistance. However, less than l.0% by weightof carbon gives only insuflicient hardness and wear resistance whileover 2.5% by weight of carbon impairs the hardenability of the alloy andreduces its ductility.

Chromium combines with carbon to form the carbides M C and M C which arevery hard, and thus plays an important role in enhancing the wearresistance of the roll. However, as the weight percentage of chromiumdecreases below 3%, the amount of these carbides is rapidly reduced. Inthe range of over 10% by weight, an excess of primary crystals ofchromium carbide appears in masses to cause exfoliation or firecrackingduring use of the roll. Therefore, the chromium percentage must becoordinated with the proportions of the other alloying elements.

Molybdenum also forms carbides, while a part thereof forms a solidsolution in the base contributing to the strength and the heatresistance at elevated temperatures. This is important since,particularly in Sendzimir mills, the surface temperature of the rolls ismomentarily raised to a substantial extent requiring a substantiallyhigh strength in the base of the roll material. This effect of thepresence of molybdenum rapidly decreases as the weight percentage isreduced below 0.5 On the other hand, as the percentage increases, theamounts of molybdenum and 3,342,058 Patented Sept. 19, 1967 its carbideincrease to give a highly improved wear resistance; however, in therange of over 8% both the workobility and the hardenability of the alloysteel are markedability and the hardenability of the alloy steel aremarked- 1y reduced.

Tungsten has substantially the same effects as molybdenum except that itraises the wear resistance of the alloy to a much greater extent thanmolybdenum. However, as the tungsten content exceeds 6% by weight, theamount of tungsten forming a solid solution in the base is increased,thereby making the roll fragile.

The use of vanadium is particular significant in the present invention.In most of the high-carbon high-chromium steels previously used,chromium carbide in primary crystals is nonuniformly distributed inmasses along the grain boundaries and such masses do .not disappear evenby subsequent working or heat treatment of the material, causingexfoliation or firecracking in the use of the roll formed of suchmaterial. Experiments have shown, however, that vanadium, if addedtogether with chromium, forms a carbide during solidification in advanceof chromium and in the form of minute spheroids to limit precipitationof the chromium carbide and thus prevents any nonuniform distribution ofcarbides in the alloy, as will clearly be observed in FIG. 2 in theaccompanying drawmg.

FIG. 2 represents two micrographs x360 of one example of the alloyaccording to the invention, which comprises 2.2% by weight of C, 0.3% byweight of Si, 0.6% by weight of Mn, 5.1% by weight of Cr, 0.85% byweight of M0, 0.9% by weight of W, and 4.8% by weight of V, the restbeing substantially iron. FIG. 2a, is a micrograph of a nonetchedspecimen oil-quenched at 950 C., showing clearly defined grains ofvanadium carbide, while FIG. 2b, represents a micrograph of a specimenoilquenched 'at the same temperature and etched with a 10% solution ofnitric acid, showing that the formation of chromium carbide iseffectively suppressed. Vanadium carbide is much harder than chromiumcarbide (about three times as hard as the latter) and thus is generallyvery effective in increasing the wear resistance of the roll. However,it is noted that the effect of the addition of vanadium is reduced toabout one half as its weight percentage is reduced below 1% while thepresence of vanadium in percentages of over 7% reduces the workabilityand hardenability of the alloy to a substantial extent.

The advantages of the roll material of the invention over thehigh-carbon high-chromium steel conventionally used as a roll materialwill be evident from FIG. 1, which graphically illustrates therelationship between the hardness and the quenching temperature of thetwo materials, and Table 1, which includes data comparing the twomaterials with respect to their wear resistance as expressed in terms oftheir resistance to grinding. The composition of the roll materialaccording to this invention forth hereinbefore in connection with FIG.2. On the other hand, the high-carbon high-chromium steel selected as atypical example of conventional roll material comprised 2.1% by weightof C, 12.5% by weight of Cr, 0.85% by weight of Mo, and 0.88% by weightof V, the balance being substantially iron. In FIG. 1, the solid linerepresents the hardness of the alloy of the invention while the dottedline represents that of the conventional high-carbon high-chromiumsteel. As observed in this figure, the alloy of the invention has anoptimum quenching temperature lower than that of the high-carbonhigh-chromium steel, thereby facilitating the hardening procedure tothat extent. It has been found in this testing that the alloyof theinvention has a satisfactory self-hardenability and exhibits excellentmechanical properties due to its finegrained structure as seen in themicrographs of FIG. 2.

TABLE 1 Weight, gr. Weight ratio, B 100% A Specific wear resistanceMaterial of specimen Material removed Grit dislodged High-C high-Orsteel.-. Inventive alloy As apparent from this table, the alloy of theinvention exhibits a notably reduced grindability compared with theconventional roll material and is duly expected to have a wearresistance nearly three times as high as that of the latter. Actual useof rolls formed of the alloy of the invention in a rolling mill fornon-ferrous alloys and in a small-sized Sendzimir mill has demonstratedthe fact that the alloy gives a highly improved roll performancecompared with any of the conventional roll materials.

We claim:

1. In a process of cold-rolling metals by means of a rolling mill havingrolls which contact the metal, the improvement in said processcomprising contacting said metals with said rolls, said rolls consistingessentially of 4 1.0 to 2.5% by weight of carbon, 3 to 10% by Weight ofchromium, 0.5 to 8% by weight of molybdenum, 0.5 to 6% by Weight oftungsten, 1.0 to 7% by weight of vanadium, not more than 0.5% by weightof silicon, not more than 0.6% by weight of manganese, the balance beingsubstantially iron and a small amount of impurities.

2. In a process of cold-rolling metals by means of a rolling mill havingrolls which contact the metal, the improvement in said processcomprising contacting said metals with said rolls, said rolls consistingessentially of 2.2% by weight of carbon, 0.3% by weight of silicon, 0.6%by weight of manganese, 5.1% by weight of chromium, 0.85% by Weight ofmolybdenum, 0.9% by weight of tungsten, 4.8% by weight of vanadium, andthe balance being substantially iron.

References Cited UNITED STATES PATENTS 2,174,286 9/1939 Gill 1262,736,650 2/1956 Grimshaw 75-126 2,867,532 l/1959 Payseen 75-l262,983,601 5/1961 Fletcher 75-126 2,996,376 8/1961 Nehrenberg 75126 OTHERREFERENCES Roberts et al.: Tool Steels, 3rd ed., Apr. 16, 1962, pub. bythe American Society for Metals, pp. 237 and 23 8,

HYLAND BIZOT, Primary Examiner.

P. WEINSTEIN, Assistant Examiner.

1. IN A PROCESS OF COLD-ROLLING METALS BY MEANS OF A ROLLING MILL HAVINGROLLS WHICH CONTACT THE METAL, THE IMPROVEMENT IN SAID PROCESSCOMPRISING CONTACTING SAID METALS WITH SAID ROLLS, SAID ROLLS CONSISTINGESSENTIALLY OF 1.0 TO 2.5% BY WEIGHT OF CARBON, 3 TO 10% BY WEIGHT OFCHRONIUM, 0.5 TO 8% BY WEIGHT OF MOLYDENUM, 0.5 TO 6% BY WEIGHT OFTUNGSTEN, 1.0 TO 7% BY WEIGHT OF VANADIUM, NOT MORE THAN 0.5% BY WEIGHTOF SILICON, NOT MORE THAN 0.6% BY WEIGHT OF MANGANESE, THE BALANCE BEINGSUBSTANTIALLY IRON AND A SMALL AMOUNT OF IMPURITIES.